1. Field of the invention
The present invention concerns a buried stripe semiconductor laser. The semiconductor structure of a laser of this kind is known internationally as a "planar buried heterojunction" (PBH) structure.
2. Description of the Prior Art
Prior art methods of manufacturing a PBH laser include so-called layer growing steps during which the semiconductor layer thickness is increased by epitaxial deposition of the material of the layers. This process is briefly as follows:
- Growth of binary composition, then quaternary composition and then binary composition semiconductor layers on a substrate. This produces a double heterostructure.
- Definition of a laser stripe in the quaternary composition layer by chemical etching from the top surface of the substrate using a dielectric mask.
- Growth of two lateral semiconductor layers to surround and bury the laser stripe.
This lateral layer growth step can employ so-called "selective" growth methods which have various drawbacks including a limited yield. Alternatively, it can employ a non-selective growth method which grows the semiconductor material not only on the sides of the laser stripe but also above the latter to create a parasitic projection. In this case it is known to grow a lift-off or stencil layer before the laser stripe is defined, the part of this lift-off layer remaining under the parasitic projection being subsequently selectively chemically attacked to separate and remove the projection. A method of this kind is described in PATENT ABSTRACTS OF JAPAN, vol. 12, No. 449 (E-686), 25 Nov. 1988 and in JP-A-63 177 493 (NIPPON TELEGR. & TELEPH. CORP. NTT) dated 21 Jul. 1988. Its efficacy seems aleatoric.
The objects of the present invention are:
- to increase the efficacy of a method of manufacturing a planar buried heterojunction laser,
- to enable the use in this method of high-yield non-selective growth methods, and
- to enable the use in this method of techniques which have advantages over the techniques previously employed.